The primary objective of the proposed research is to identify and characterize specific plant proteins that represent host factors required for the successful infection of Arabidopsis by a geminivirus, beet curl top virus (BCTV). The interaction of BCTV with Arabidopsis represents a powerful model system that will allow a combination of biochemical, molecular and genetic approaches to be applied to the detailed analysis of the molecular basis of viral pathogenesis. The major specific aims of the proposed research are 1) to use positional cloning strategies to isolate naturally occurring BCTV resistance and hypersusceptibility genes from several Arabidopsis ecotypes; 2) to isolate and characterize Arabidopsis mutants that have become resistant to BCTV infection; and 3) to use the yeast two hybrid system to identify specific Arabidopsis cDNAs that encode proteins that interact with BCTV proteins. The proposed studies will allow the identification of specific host factors that play important roles in the life cycle of a viral pathogen. To date, none of these host factors has been clearly identified for any plant virus. The identification of specific host factors, and a detailed characterization of how these host factors interact with viral encoded proteins, will provide significant new information concerning the mechanisms whereby viruses integrate their life cycle into the metabolism of its host. These studies are likely to provide novel insights into the effects of viral infection on major host regulatory systems such as the control of gene expression and DNA replication and how viruses move from cell to cell to systemically infect a host. The proposed studies will be particularly relevant to developing strategies aimed at interfering with the infection of eukaryotic cells by viral pathogens.